1. Field of Invention
This invention relates to a device and method for comma detection and word alignment in serial transmission. More particularly, this invention relates to a pipeline architecture applied in a gigabit network environment for completing data comparison of comma detection and data output of word alignment in two stages during the process of converting a serial data into a parallel data. The invention is a device and method for increasing the data transmission bandwidth and efficiency.
2. Related Art
The current gigabit serial transmission network covers a wide area, including the optical network technology, the gigabit network technology, the Infiniband transmission technology, the serial ATA and the PCI Express. The data transmissions in these high-speed serial links all use 8/10 code proposed by A. X. Widmer and P. A. Franazek. Such a code set includes all 8-bit data codes (256 unique data characters) and additional special (or “K”) symbols. Since this code set is inherited with the abilities of DC-balancing, limited run length coding, and error bit detection, the code set is widely used in high-speed serial transmissions. The ability of DC-balancing refers to the equality of the numbers of 1 and 0 in the serial data bits. The limited run length coding means that the number of continuous 1 or 0 does not exceed five in the serial data, ensuring correct extraction of clocks by the receiving end from the serial data stream.
In practice, the transmission end of the serial links represents a character using 10 bits in data coding. The receiving end of the serial links has to use 10 bits as the unit to perform symbol comparison. If the received symbol is the same as a code, then the symbol is interpreted as the corresponding 8-bit data. For the receiving end, it is especially important to obtain correct 10 bits for decoding. Among the code sets, some special symbols have particular bit combinations called commas. These commas are capable of making the receiver obtain correct word alignment in the serial bit stream. Since the commas are unique in coding, arbitrarily coded serial data may not have the same bit combination as the commas. The receiving end can thus determine the boundaries of words.
In the prior art, the transmitted serial data take 10 bits as a unit to represent a character. However, the boundaries of each 10 bits are determined through the comma detection so that correct conversion to parallel data is possible. Incorrect bit boundaries will result in erratic data interpretation. Therefore, a comma comparison circuit is used to detect the correct bit boundaries. Once the comparison circuit finds the correct boundaries in the serial bit stream to accomplish word alignment, the data are transmitted in a parallel way out of an output circuit. Consequently, the more time it takes to perform comma detection and word alignment, the less time is allowed for the next stage circuit to receive word data.